By glycerol is meant a glycerol either purified or not, preferably stemming from biomass and notably a highly purified or partly purified glycerol. A purified glycerol has a purity greater than or equal to 98%, obtained by distillation of glycerine. A non-purified or only partly purified glycerol may be in solution in methanol when it for example stems from transesterification of triglycerides, as described hereafter. By glycerine is notably meant glycerine of natural origin, stemming from hydrolysis of vegetable oils and/or animal fats, or more or less purified or refined or else raw glycerine of synthetic origin stemming from petroleum. As an example, raw glycerine has a titer comprised between 80 and 85%. Thus, subsequently in the description, reference is mainly made to the conversion of a glycerol or a glycerine stemming from biomass, but the invention of course is not limited thereto and its benefit extends to all glycerols and glycerines, regardless of their origins and their degrees of purity.
Gradual exhaustion of fossil energies leads industrials to envision the use of renewable raw materials stemming from the biomass for producing fuels. In this context, biodiesel is a fuel produced from vegetable or animal oil.
This product benefits from a green aura because of a clearly favorable CO2 balance as compared with fossil energies. Diester® (or MEVOs, Methyl Esters of Vegetable Oils) is a biodiesel made by transesterification of triglycerides present in oleaginous liquids, notably palm, rapeseed and sunflower vegetable oils, by methanol. This transesterification co-produces approximately and according to the contemplated methods, 100 kg of glycerol per metric ton of diester®. The non-lipid portion of the raw material used, the cakes, is mainly exploited in animal feed.
This biodiesel is used, mixed with diesel oil. European Directives 2001/77/EC and 2003/30/EC, which will be applied in the near future, plan to introduce 7% in 2010 and 10% by the year 2015 of diester® in diesel oils. This substantial increase in the produced amount of biodiesel will generate significant amounts of glycerol equivalent to several hundreds of thousands of tons/year.
Some 1500 uses of glycerol have already been listed, among which the following illustrate its presence in many and various formulations, as examples:                moisteners in pharmacy (in suppositories and syrups) or in cosmetology in moisturizing creams, glycerine soaps, toothpastes,        solvents in the food industry,        plasticizers or lubricants in the chemical industry.        
These applications will prove to be clearly insufficient for absorbing the amounts of glycerol which will be co-produced with biodiesels and although in progress, the conventional glycerol market (soaps, pharmacy, . . . ) will not be able either to absorb such a surplus. It is therefore vital to find new applications with which the value of very large volumes of glycerol may be increased.
In view of this, many outlets have been investigated these recent years (see M. Pagliaro et al, Angew. Chem. Int. Ed. (2007) 46, 4434-4440 as well as M. Pagliaro, M Rossi: The Future of Glycerol, RSC Publishing, Cambridge (2008)), with in particular the six following routes for adding value thereto:                conversion into 1,3-propanediol and into 1,2-propanediol, notably used as base monomers in the synthesis of polyesters and polyurethanes,        conversion into monoesters for the chemistry of lubricants,        conversion into polyglycerols used as emulsifiers, food additives,        conversion into acrolein (by dehydration) and into acrylic acid (by dehydration and oxidation),        direct addition of value as additives for animal feed.        
Acrolein and acrylic acid are traditionally used by controlled oxidation in the gas phase of propylene by oxygen from air in the presence of catalysts based on molybdenum and/or bismuth oxides. The thereby obtained acrolein may either be directly integrated into a two-step method for producing acrylic acid, or be used as a synthesis intermediate. The production of both of these monomers is therefore closely related to propylene which in substance is produced by steam cracking or catalytic cracking of petroleum cuts.
The markets of acrolein, one of the simplest unsaturated aldehydes, and of acrylic acid are gigantic since these monomers enter the composition of many mass marketed products.
Moreover, acrolein, a highly reactive compound because of its structure, finds many applications, notably as a synthesis intermediate. It is most particularly used as a key intermediate entering the synthesis of D,L-methionine and of its hydroxyl-analog derivative, 2-hydroxy-4-methylthiobutanoic acid (HMTBA). These food additives are massively used since they enter the composition of food supplements indispensable to the growth of animals (poultry, pigs, ruminants, fish, . . . ). In a certain number of cases, it may be profitable to be able to increase, or even ensure production capacities of existing industrial units by diversifying the engaged raw material. It therefore appears to be most particularly of interest to be able to increase acrolein productivity, while reducing the dependency towards this resource stemming from petroleum which is propylene.